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Author Topic: motive power  (Read 8979 times)

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« Reply #15 on: November 22, 2012, 09:28:42 PM »

Your engine, or motor, or unit, will not function without some sort of motive power.
Engines and motors do not create motive power but rather they create work.

Some words, terms, and phrases have evolved to encompass other meanings.
The true meaning of the phrase has been muddied.
You can label something pretty much whatever you want nowadays, like Rich says “not a big deal”.

If you want to call a diesel or steam engine or motor, motive power, that’s ok with me.
 I’ll still have a general idea of what you’re talking about.
Toy train locomotives are a far stretch from motive power, but call it what you will.
Rule #1 applies. Be happy in your designated label.

And a question for the teach…

What is the form of motive power for a steam locomotive?
a)   Water
b)   Fire
c)   Steam
d)   a and b
e)   a and c
f)   b and c
g)   all of the above
h)   none of the above
i)              the steam engine is of itself the motive power

There is a bonus slice of pumpkin pie today if you get it right.
Happy Thanksgiving

Technically, where I come from, the "engine" parts of a "steam engine" are the cyclinders, motion and wheels.  They are the "engine" as they provide the movement.

The boiler and firebox provide the fuel that powers the steam engine.  i.e. the steam.

Or, a steam locomotive produces its power through a steam engine. The locomotive is fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler.  It's the steam pruduced by the boiler which drives the steam engine.  The engine consisting of the cylinders, valve gear (motion), frame and driving wheels.

To Quote Wiki: -

In thermodynamics, motive power is an agency, such as water or steam, used to impart motion. Generally, motive power is defined as a natural agent, as water, steam, wind, electricity, etc., used to impart motion to machinery; a motor; a mover. The term may also define something, as a locomotive or a motor, which provides motive power to a system. In current use, motive power may be thought of as a synonym for either "work", i.e. force times distance, or "power", an effect producing motion, depending on the context of the discussion.



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« Reply #16 on: November 28, 2012, 05:26:19 AM »

Wow! Thank you all for your helpful responses.  I generally only fool with the computer when it is quiet at work, thus the delay in my response. Smiley

I am experienced aircraft modeler, but I am learning a new vocabulary related to trains, which is part of the fun.

Thanks again!

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« Reply #17 on: November 28, 2012, 12:14:19 PM »

Now we can split hairs and parse words! Smiley

In my experience in railroading, "motive power" means "locomotive".  This is not a physics definition, but a railroad definition.  A locomotive is an independently controlled unit or linked group of units, capable of moving cars, propelled by any form of energy.

Under these definitions, "motive power" refers to any locomotive propelled by any form of energy.

Water and fire are not motive power.  In a steam locomotive, water only plays an intermediate role in allowing the chemical bond energy in fire to be transformed into mechanical force.  Water does not do this by loosening its own chemical bond energy, but instead does this by changing its state of matter from a liquid to a gas.

Fire releases chemical bond energy of the fuel.  This bond energy in the fuel is the ultimate source of power in a heat engine.

Same goes for internal combustion engines, except for them, water is not needed as an interim means of transferring energy.  The bond energy in the fuel is converted to mechanical energy in the engine, then converted to electrical energy in the generator, then converted once more into mechanical energy in the motors.

An electric locomotive draws ready-made electricity and converts it into mechanical energy in its motors.  As its power source arrives ready to use, it is not an "engine".  But it is a locomotive.

As has been pointed out, a steam locomotive usually has only one steam "engine", but could have two or (rarely) more.

Steam is not fuel.  Chemical bond energy is not released in steam.  Steam is a transmission fluid.

In an internal combustion locomotive, the engine itself (Diesel or turbine) is referred to as the "prime mover".  It is the original place where chemical bond energy in the fuel is converted to mechanical energy.  Steam locomotives do not have a prime mover.  The chemical bond energy of the fuel is converted to steam in the boiler, but is not converted to mechanical energy until it gets to the engine.

Electric locomotives do not contain a prime mover.  The prime mover sits back in the stationary power station.


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« Reply #18 on: November 29, 2012, 12:41:31 AM »


Don't forget that steam expands in the cylinders!

Also, the ultimate source of power for an electric locomotive isn't the catenary or other electrical supply; it's hydro, coal, oil, gas, nuclear, solar/wind or even tidal.

                                                             -- D
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